A radioimmunoassay for chlorinated dibenzodioxins has been developed. One version of the assay responds to between 20 and 200 pg of dioxin, but is subject to interference. Another version responds to between 90 pg and 10 ng of dioxin. An adequate assay for mono-2-ethylhexyl phthalate in plasma has been completed. Several antisera to specific PCB isomers have been raised and are being characterized. Attempts are being made to raise an antiserum specific for dibenzofurans. Techniques for the presentation of these water-insoluble substances to the necessarily aqueous antibodies are being refined.